Developers and web designers need to check this post regarding the shutdown of Google+ API:

Quote:

Google+ APIs will be shut down on March 7, 2019. This includes Google+ Sign-in and OAuth token requests with Google+ scopes. Learn more.
Google+ integrations for web and mobile apps will also cease to function March 7, 2019. Learn more.

This will be a progressive shutdown, with intermittent failures starting as early as January 28, 2019.